<html>
  <body>
    <canvas id="canvas"></canvas>
    <script>
      const canvas = document.getElementById('canvas')
      const ctx = canvas.getContext('2d')

      ctx.fillStyle = 'rgba(255,0,0,255)'
      ctx.fillRect(10, 10, 150, 100)
    </script>
  </body>
</html>
